Apparatus for fabricating synthetic resin articles by double rotation of a mold

ABSTRACT

An apparatus for fabricating synthetic resin articles by double rotation of molds wherein a plurality of molds are rotatably supported on a frame by rotation shafts for effecting their rotation and the frame is rotatably mounted on a support truck by revolution shafts for effecting the revolution of the frame and consequently the molds. The frame is fitted with drive shafts and there are provided rotation force transmitting devices between the revolution shafts and drive shafts as well as between said drive shafts and rotation shafts. The axial lines of said rotation and revolution shafts perpendicularly intersect each other substantially at the gravitational center of the articles being fabricated in the molds, and double-chain drive means is provided to impart rotation to the revolution shafts and consequently to the rotation shafts via the rotation force transmitting devices, the drive means being disposed at a position external of the truck and outside of the mold heating and cooling sections of the apparatus.

United States Patent 1 Suzuki Jan. 29, 1974 APPARATUS FOR FABRICATINGSYNTHETIC RESIN ARTICLES BY DOUBLE ROTATION OF A MOLD [75] Inventor:Tadao Suzuki, Toyohashi, Japan [73] Assignee: Denki Kaguku KogyoKabushiki,

Kaisha, Tokyo, Japan .[22] Filed: Mar. 30, 1972 [21] Appl. No.: 239,651

[52] US. Cl 425/429, 425/430, 264/310 [51] Int. Cl. B29c 5/04 [58] Fieldof Search 425/425, 429, 430, 435; 264/310, 311

[56] References-Cited UNITED STATES PATENTS 1,812,242 6/1931 Jensen425/430 3,507,950 4/1970 Barnett et al. 264/310 2,629,131 2/1953 Martinet al. 264/310 X 2,967,329 l/l961 Friedland et a1... 264/310 3,234,3152/1966 Blue et al 264/310 3,337,662 8/1967 Spencer 425/429 X 3,676,0377/1972 Pivar 425/435 Primary Examiner-Robert L. Spicer, Jr. Attorney,Agent, or Firm-Flynn & Frishauf An apparatus for fabricating syntheticresin articles by double rotation of molds wherein a plurality of moldsare rotatably supported on a frame by rotation shafts for effectingtheir rotation and the frame is rotatably mounted on a support truck byrevolution shafts for effecting the revolution of the frame andconsequently the molds. The frame is fitted with driveshafts and thereare provided rotation force transmitting devices between the revolutionshafts and drive shafts as well as between said drive shafts androtation shafts. The axial lines of said rotation and revolution shaftsperpendicularly intersect each other substantially at the gravitationalcenter of the articles being fabricated in the molds, and double-chaindrive means is provided to impart rotation to the revolution shafts andconsequently to the rotation shafts via the rotationforce transmittingdevices, the drive means being disposed at a position external of thetruck and outside of the mold heating and cooling sections of theapparatus.

ABSTRACT 6 Claims, 3 Drawing Figures m g a PATENTED JAN 2 91974 SHEET 3BF 3 FIG. 3

APPARATUS FOR FABRICATING SYNTHETIC REsIN ARTICLES BY DOUBLE ROTATION OFA MOLD This invention relates to an apparatus for fabricating syntheticresin articles by double rotation of molds which carries out the moldingof thermoplastic synthetic resin charged in the molds by their rotationand revolution.

The known' rotational molding method consisted in charging powders ofthermoplastic synthetic resin in a mold and rotating the closed moldunder heating to melt and deposit the resin powders on the surface ofthe mold cavity in uniform thickness, thereby fabricating hollowmoldings true to the shape of the mold cavity. The piror art rotationalmolding method includes mono-rotation system wherein the mold is rotatedabout a single axis and a double rotation system wherein the mold isrotated about two axes simultaneously. The conventional method wasintended to fabricate hollow moldings mainly from powders of syntheticresin. Therefore, attention has heretofore been paid centrifugally topress resin powders against the inner walls of the mold cavity. Since itdecreased production eff ciency to mold only one article pre-heatingcycle, the customary practice was to provide a large number of molds tofabricate numerous moldings at a time. With the conventional doublerotational molding system, many juxtaposed molds were simultaneouslydriven about the axes of rotation and revolution, that is, subjected tothe so-called double rotation. Since it was difficult to rotate themolds so as to realize the proper intersection of the axes of rotationand revolution therein, there has heretofore been used that type ofrotational molding system wherein the axes of rotation and revolution ofthe molds did not intersect each other in the molds. Therefore,'suchsystem rather resulted in the complicated rotation mechanism, failing toproduce moldings of uniform formation free from uneven wall thicknesses.

This invention has been accomplished in view of the aforementionedcircumstances and is intended to provide a rotational molding apparatusfor molding thermoplastic synthetic resin articles of uniform formationfree from uneven wall thicknesses. The apparatus comprises a pluralityof molds fitted with shafts for effecting their rotation; 21 frame forrotatably supporting the molds through said shafts; support stands forrotatably supporting the frame through shafts fitted thereto foreffecting the revolution of the molds; drive shafts separately mountedon the frame; and a rotating force transmitting means disposed betweenthe mold revolution shafts and drive shafts as well as between saiddrive shafts and mold rotation shafts, wherein the axial lines of therotation and revolution shafts of each mold perpendicularly intersecteach other in the mold substantially at the gravitational center of amolding being fabricated therein. To effect efficient molding by thecontinuous heating and cooling of the molds, the frame bearing the moldsis rotatably mounted on a movable truck which is made to travel throughthe divided sections of its course, that is, a raw material feedingsection, mold heating section and mold cooling section; and the moldsare continuously heated and cooled while making rotations andrevolutions by means of a circulating chain disposed at a prescribedlocation.

The present invention can be more fully understood from the followingdetailed description when taken in FIG. 1 is a front elevation, partlyin section, of a rotational molding apparatus according to an embodimentof this invention;

FIG. 2 is a perspective view, partly in section, of a rotational moldingapparatus according to another embodiment of the invention; and

FIG. 3 is a plan view of the apparatus of FIG. 2 with part thereof shownin enlargement.

There will now be described by reference to the appended drawings arotational molding apparatus according to the preferred embodiments ofthis invention. Referring to FIG. 1, numeral 1 represents a moldsplittable at the center into two parts which jointly define a sphericalcavity. FIG. I typically illustrates two juxtaposed spherical molds.Numeral 2 shows a rectangular frame, and 3 denotes a pair of shaftsprojectively fitted at the opposite points of the periphery of each mold1 so as to effect its rotation, the mold being rotatably fixed to theinside of the frame 2 by said shafts 3. The frame 2 is provided on theopposite sides with a pair of shafts 4 for carrying out the revolutionof the molds l. The mold revolution shafts 4 are so disposed as to havethe axial line thereof perpendicularly intersected by that of the moldrotation shafts 3 at a point M substantially conforming with thegravitational center of the spherical molds 1. Numeral 5 shows thebearing sections of the mold revolution shafts 4. The bearing sections 5are mounted on a pair of support stands 6, causing the frame 2 to berotatably fitted to said support stands 6 through the mold revolutionshafts 4. Numeral 7 is a motor, 8 a speed change gear, and 81 a sprocketfixed to the output shaft of said speed change gear 8. Numeral 42 is asprocket fitted to one of the mold revolution shafts 4 to be connectedto the aforesaid sprocket 81 by a chain 9. Numeral 10 representssprockets fixed to the bearing section 5 of the other mold revolutionshaft 4, and numeral 11 denotes drive shafts rotatably supported byprojections 12 formed on the frame 2. Numeral 13 is a sprocket attachedto one end of the drive shafts l1, numeral 14 a chain for connecting thesprocket 13 with the sprockets 10, numeral 15 bevel gears fixed to theother end of the drive shafts 11, and numeral 16 bevel gears fitted tothe mold rotation shafts 3 for engagement with the former bevel gears15.

When there is driven the motor 7 described above, then the moldrevolution shafts 4 are rotated through the sprocket 81, chain 9 andsprocket 42 in turn, causing the molds l to revolve with the frame 2about an axial line 41. At the same time, the chain 14, sprocket l3,drive shafts l1 and bevel gears 15 and 16 rotate in turn through thesprocket 10 fixed to the bearing section 5, causing the molds 1 torotate about the axial line 31. That is, the molds 1 are driven by themotor 7 to make rotations about the axial line 31 and revolutions aboutthe axial line 41. When the mold '1 charged with a proper amount ofthermoplastic synthetic resin is heated from around while it is rotatingand revolving, then the resin is pressed against the walls of the moldcavity by gravitational and centrifugal forces to be melted thereon,forming a spherical molding whose outline exactly conforms with theinner shape of the mold cavity. Immediately after completion of molding,

the mold l is transferred to the cooling section. After cooling, themold l is opened to take out a desired spherical molding.

Provided it is of thermoplastic type, the synthetic resin used may be inthe form of powders or pellets. If the mold l is charged with suchamount of nonfoamable resin as does not completely fill up the moldcavity, then there will be obtained a hollow molding. In contrast, wherefoamable resin is used, there will be produced a solid foamed molding.

The rotational molding apparatus of this invention is applicable notonly to molds having a spherical cavity, but also to those having manyother forms of cavities, thus freely fabricating moldings of othershapes than the spherical. The foregoing description referred to thecase where there were prvided two molds. If, however, three or moremolds are mounted on a larger frame by fitting an increasing number ofbevel gears to the drive shafts 11, then the molding efficiency will beprominently elevated.

According to the aforementioned rotational molding apparatus of thisinvention, the molds 1 are rotatably fitted to the frame 2 through theshafts 3 for effecting their rotation. The frame 2 is rotatably mountedon the support stands 6 through the mold revolution shafts 4.Accordingly, the molds l are made to rotate and revolve about the axiallines 31 and 41 perpendicularly intersecting each other substantially attheir gravitational center. Thus the synthetic resin-charged in the mold1 is, when melted, uniformly deposited on the inner walls of the moldcavity by gravitational and centrifugal forces without being undulyaccumulated in particular portions of the mold cavity. When, therefore,there is fabricated a hollow molding from nonfoamable resin, the producthas a uniform formation free from uneven wall thicknesses.

Further, with the apparatus of this invention, the axial lines 31 and 41of the rotation and revolution shafts 3 and 4 of the molds 1perpendicularly intersect each other substantially at the gravitationalcenter of moldings being fabricated in the molds, preventing the frame 2from being subjected to an abnormal gravitational and centrifugal forceresulting from their eccentric rotation which might otherwise occur.Moreover, the apparatus of the invention can have its molds rotated andrevolved with a small physical force, thus reducing thepowerrequirement. Though the rotation shaft 3 and revolution shaft 4 of themold 1 may receive a force acting in the radial direction of the shafts,these shafts 3 and 4 are substantially free during rotation from anycentrifugal force that would tend to displace them in the axialdirection of their own, thereby permitting the smooth rotation andrevolution of the mold 1 due to a construction chiefly based on a radialbearing. Even where, therefore, there is used a large mold, syntheticresin articlescan be molded efficiently by a simple mechanicalarrangement. When the motor 8 rotates the mold revolution shafts 4, thenthe drive shafts l1 interlockingly operate the mold rotation shafts 3,so that the rotation and revolution of the mold 1 can be effected byonly one motor. The mechanism for interlocking the drive shafts 11 withthe rotation and revolution shafts 3 and 4 of the molds l, and therevolution shafts 4 with the motor 8 is not limited to the drivetransmission devices shown in FIG. 1, but may consist of other drivetransmission devices, for example, a gear assembly or belt.

If there is used with the molding apparatus of FIG. 1 a mixture of fineand coarse granules of raw synthetic resin, or a mixture of rawsynthetic resin particles of different densities, then there can beeasily fabricated a molding consisting of two inner and outer layersseparated according to the different particle sizes or densities of saidraw resins.

Where it was previously desired to produce such two inner and outerlayers, the prior art apparatus failed to separate them clearly. incontrast, the apparatus this invention can effect said separation quitedistinctly.

Further, the apparatus of the invention can mold a rigid hollow articlefrom nonfoamable synthetic resin in the following manner. Namely, thereis separately fabricated a spherical reinforcement body having itsperiphery bored with numerous apertures larger than the particle size ofpowders of the aforesaid nonfoamable synthetic resin being later placedtherein. The perforated spherical body thus charged is put in a mold.

When the mold is fitted to the apparatus of the invention and latersubjected to rotation and revolution under heating, then said resinpowders contained in the perforated spherical body are forcefully drawnout from the interior thereof through the apertures bored in theperiphery by centrifugal and gravitational forces applied to the mold tofill up a space defined between the mold cavity and the outer surface ofsaid spherical body in molten form and tightly deposited on said outersurface. When, therefore, released from the mold, the molding thusfabricated constitutes a rigid hollow article with the core of thespherical reinforcement body fully coated with said nonfoamable resin.

If, in this case, there is used a slightly excess amount of resinpowders, part thereof will remain in the spherical reinforcement body toplug its apertures instead of being drawn out therethrough. Accordingly,molten resin coatings on the inner and outer walls of said sphericalbody are joined together through the apertures thereof, thus producing amore rigid hollow article with said spherical body as a core.Manufacture of such a molding is one of the features of the apparatus ofthis invention.

Referring to FIG. 2, numeral 1 represents a spherical mold splittable atthe center into two half portions. Numeral 2 denotes a frame to whichthe mold l is fitted so as to rotate by a pair of mold rotation shafts 3projectively provided at the opposite points of its periphery. Numeral20 is a support truck for rotatably supporting the frame 2 through moldrevolution shafts 4 fitted thereto. Numeral 21 is a rail track on whichthe truck 20 travels. The course of the truck 20 along the rail trackv21 is divided into three a, b and c sections, that is, a raw materialfeeding section, mold heating section and mold cooling section. Numerals22 and 23 are circulating chains. One circulating chain 22 advances thetruck 20 bearing the mold 1 through the aforesaid three a, b and 0sections in turn. When said truck 20 approaches theheating section b,the other circulating chain drives the sprocket 42 fitted to one side ofthe truck 20 by having its links engaged with the projections of saidsprocket 42, said sprocket 42 being connected to the mold revolutionshafts 4. Accordingly, the frame 2 is made to rotate on the truck 20 forthe revolution of the mold 1.

As illustrated in enlargement in FIG. 3, a chain 14 7 causes theaforesaid mold revolution shaft 4 to interlock with the drive shaft 11separately mounted on the frame 2. Said drive shaft 11 is connected tothe mold rotation shaft 3 through bevel gears and 16. There fore, thecirculation of the chain 23 eventually leads to the interlockingoperation of the drive shaft 11 through the rotation of the aforesaidsprocket 42 and mold revolution shaft 4 resulting from the circulationof the chain 23. Consequently, the mold 1 rotates about its rotaionshaft 3 on the frame 2 through the engagement of the aforementionedbevel gears 15 and 16. Accordingly, the mold 1 travels on the rail track21 while making rotations and revolutions about its rotation andrevolution shafts 3 and 4 whose axial lines perpendicularly intersecteach other in the mold 1. At the points on the travelling course of thetruck where the sprocket 42 begins to rotate by engagement with thecirculating chain 23 and where the sprocket 42 stops its rotation, it ispreferred that the rail track 21 be formed of an inclined section so asto allow the sprocket 42 to be easily engaged with or disengaged fromthe circulating chain 23 according as the truck 20 moves down or up saidinclined section.

The truck 20 travels on the rail track 21 by engagement between pawls 24spatially fixed to the chain 22 and a pawl 25 attached to the oppositeside of the truck 20 to that on which there is provided the aforesaidsprocket 42. Further, it is desired that the rail track 21 at thoseparts of the travelling course of the truck 20, where both pawls 24 and25 are engaged with or disengaged from each other be formed of aninclined section so as to cause the truck 20 to be easily engaged withor disengaged from the chain 22, according as thetruck 20 moves down orup said inclined section.

As apparent from FIG. 2, while the truck 20 carrying the mold stays atthe first half part of the raw material feeding section a, neither thetruck 20 is made to travel by the chain 22, nor the mold I mountedthereon is caused to make any rotation or revolution by the chain 23. Atsaid first half part of the raw material feeding section a, the mold 1is charged with foamable or nonfoamable synthetic resin in the form ofpowders or pellets as previously described. Where the resin usedconsists of pellets, they should preferably be several millimeters orabout one centimeter in diameter. When the charging of raw resin iscompleted, the truck 20 is made to advance to the succeeding heatingsection b by the chain 22 through the second half part of said feed ingsection a. When the truck 20 is brough to the heating section b, thesprocket 42 engages the circulating chain 23 to carry out the rotationand revolution of the mold 1. The heating section b has a dome 26covering its whole and doors 27 provided at both ends. Within the dome26 is disposed means 28 for heating the mold 1. The mold 1 travelstogether with the truck 20 by the chain 22 and is heated while makingrotations and revolutions. After leaving the heating section b, thetruck 20 is transferred to the cooling section c, where the mold 1 iscooled by water ejected from spray 29, while making rotations andrevolutions. After the mold 1 is cooled, the truck 20 further travels onthe rail track 21 to a place to which the chain 23 of the coolingsection c does not extend, thereby stopping the rotation and revolutionof the mold 1. When the resin in the mold 1 is fully molded, it isopened to take out the product.

FIGS. 2 and 3 jointly illustrate the case where there is mounted onlyone mold on the truck 20. However, it is of course possible to providetwo or more molds as in FIG. 1. Such arrangement is particularly adaptedto elevate the efficiency of producing moldings.

The rotational molding apparatus of this invention shown in FIGS. 2 and3 causes the mold 1 to travel with the truck 20 while making rotationsand revolutions, enabling the mold 1 to be heated and cooled insequential steps, with the resultant increase in molding efficiency.Further, the rotation and revolution of the mold 1 is effected by achain which is constructed of nonflammable material such as metal andconsequently is prevented from being burnt, though it is exposed to thehigh temperature of the heating section b, so that said rotation andrevolution can always be reliably carried out. The travel of the truck20 which is carried out also by means of a chain can be smoothlycontrolled by readily engaging the truck 20 with the chain ordisengaging it therefrom by the previously described special device. Thechain 23 for effecting the rotation and revolution of the mold 1 and thechain 22 for driving the truck 20 are operated independently of eachother, so that their running speed can be freely varied, enablingproduction of various types of molding having different wall thicknessesand different volumes. Further, at the latter part of the raw materialfeeding section a, the truck 20 alone is allowed to travel with the mold1 prevented from making any rotation and revolution, and at the latterpart of the cooling section c, the mold 1 alone is allowed to makerotations and revolutions with the travel of the truck 20 stopped,thereby facilitating the charging of raw material and the cooling of themold 1. In the apparatUs of FIGS. 2 and 3, the axial lines of therotation and revolution shafts of the mold 1 perpendicularly intersecteach other in the mold 1 as in the apparatus of FIG. 1, obviouslyoffering the same prominent advantage as described in connection withthe apparatus of FIG. 1.

Where there is no need to vary the running speed of both chains 22 and23 of FIG. 2, there may be used only one chain instead of two, causingsaid single chain concurrently to undertake the travel of the truck 20and the rotation and revolution of the mold 1.

I claim:

1. Apparatus for fabricating synthetic resin articles by double rotationof a mold comprising:

a mold;

a generally rectangular frame for rotatably supporting said mold;

a support truck for rotatably supporting said frame;

rotation shafts extending from said mold and rotatably coupled to thelonger sides of said frame, and revolution shafts extending from theshorter sides of said frame and rotatably coupled to said truck, saidrotation and revolution shafts being so arranged as to have their axesintersecting substantially perpendicularly at about the gravitationalcenter of said resin article;

sprocket means on said truck and drivingly coupled to at least one ofsaid revolution shafts;

a drive shaft rotatably mounted on, and substantially in parallel with,one of the longer sides of said frame and transmitting rotary motion ofsaid revo lution shafts to said rotation shafts through transmissionmeans;

a rail track for guiding said support truck;

a chain means provided for moving said truck on said track from a rawmaterial feeding section to a mold heating section and a mold coolingsection;

a heating device provided in said mold heating section to heat saidmold;

another chain means provided at least in said mold heating section forengaging said sprocket when said truck is in said heating section forrotating said revolution and rotation shafts, thereby simultaneouslyrotating and revolving said mold at least in said mold heating section;and

drive means for' driving said chains and disposed at a position outsidesaid three sections and external of said truck.

2. Apparatus according to claim 1 including one mold.

3. Apparatus according to claim 1 including a plurality of molds,

4. Apparatus according to claim 3 wherein each of said plurality ofmolds have rotation shafts extending 5. Apparatus according to claim 4wherein the rotation shafts of each of saidmolds receives rotary motionfrom respective drive shafts mounted to a longer side of said frame.

6. Apparatus according to claim 1 wherein said transmission meanscomprises gear means coupled to said drive shaft, and a mating gearmeans coupled to one of the rotation shafts extending from said mold.

1. Apparatus for fabricating synthetic resin articles by double rotationof a mold comprising: a mold; a generally rectangular frame forrotatably supporting said mold; a support truck for rotatably supportingsaid frame; rotation shafts extending from said mold and rotatablycoupled to the longer sides of said frame, and revolution shaftsextending from the shorter sides of said frame and rotatably coupled tosaid truck, said rotation and revolution shafts being so arranged as tohave their axes intersecting substantially perpendicularly at about thegravitational center of said resin article; sprocket means on said truckand drivingly coupled to at least one of said revolution shafts; a driveshaft rotatably mounted on, and substantially in parallel with, one ofthe longer sides of said frame and transmitting rotary motion of saidrevolution shafts to said rotation shafts through transmission means; arail track for guiding said support truck; a chain means provided formoving said truck on said track from a raw material feeding section to amold heating section and a mold cooling section; a heating deviceprovided in said mold heating section to heat said mold; another chainmeans provided at least in said mold heating section for engaging saidsprocket when said truck is in said heating section for rotating saidrevolution and rotation shafts, thereby simultaneously rotating andrevolving said mold at least in said mold heating section; and drivemeans for driving said chains and disposed at a position outside saidthree sections and external of said truck.
 2. Apparatus according toclaim 1 including one mold.
 3. Apparatus according to claim 1 includinga plurality of molds.
 4. Apparatus according to claim 3 wherein each ofsaid plurality of molds have rotation shafts extending therefrom, saidrotation shafts being rotatably coupled to the longer sides of saidframe, said rotation shafts each being so arranged as to have theirrespective axes intersecting substantially perpendicularly with saidrevolution shafts at about the gravitational center of said resinarticle to be formed in the mold, said rotation shafts receiving rotarymotion from said revolution shafts via at least one drive shaft mountedon, and substantially in parallel with, a longer side of said frame. 5.Apparatus according to claim 4 wherein the rotation shafts of each ofsaid molds receives rotary motion from respective drive shafts mountedto a longer side of said frame.
 6. Apparatus according to claim 1wherein said transmission means comprises gear means coupled to saiddrive shaft, and a mating gear means coupled to one of the rotationshafts extending from said mold.